Non-roughening microporous laminate and process for producing the same



Dec. 24, 1968 R. v. EINSTMAN 3,413,198

NON-ROUGHENING MICROPOROUS LAMINATE AND PROCESS FOR PRODUCING THE SAME Filed Nov. 14, 1966 INVENTOR ROBERT V. EINS'I'IMAN AGENT United States Patent 3,418,198 NON-ROUGHENTNG MICROPOROUS LAMINATE AND PROCESS FOR PRODUCING THE SAME Robert V. Einstrnan, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware Continuation-impart of application Ser. No. 350,056, Mar. 6, 1964. This application Nov. 14, 1966, Ser. No. 594,122

18 Claims. (Cl. 16184) ABSTRACT OF THE DISCLOSURE A process for producing a non-roughening microporous laminate useful as a leather replacement by:

(a) coating a surface of a porous fibrous web with a liquid dispersion of a polymeric component and a solvent therefor; the dispersion having a viscosity high enough to permit its retention by the web under the coating conditions and low enough to permit complete penetration of the web under the conditions of step (b) below in which the opposite surface of the web is in contact with a flexible porous fibrous substrate sheet;

(b) applying suction to the free surface of the substrate sheet which draws the dispersion through the porous web and at least partially into the substrate sheet to form a laminate; and

(c) bathing and drying the resulting laminate.

This application is a contiuuation-in-part of the copending application Ser. No. 350,056, filed Mar. 6, 1964, now abandoned.

This invention concerns a method for producing laminates, and more particularly, to a process for preparing a laminate of a microporous sheet material useful for shoe uppers.

One of the problems encountered during the lasting operation when forming shoes from a material prepared by impregnating and coating a fibrous web is the development of roughness in those areas which require some stretching over the last such as in the toe and quarter areas of the shoe. Even when a non-woven web is used, this roughening is usually present and is associated with the pattern that results from needling the non-woven web prior to impregnation.

One object of this invention is to provide new laminates having exceptional resistance to delamination.

It is a particular object of this invention to produce a microporous sheet material for shoe uppers from a fibrous web, that has a pattern on its surface prior to impregnating and surface coating, which microporous sheet material is non-roughening in the sense that after the fibrous web is impregnated, coated and then stretched, as during toe and quarter lasting during shoe manufacture, a surface pattern is not visually apparent.

In accordance with this invention, plied porous sheets are securely bonded with a polymeric impregnant to form a laminate having exceptional resistance to delamination. By utilizing appropriate fibrous webs as starting materials, this invention provides a strong coriaceous product particularly useful in preparing shoe uppers and characterized by superior non-roughening and scuff-resistance properties.

The process of this invention can be aptly illustrated by a preferred embodiment which comprises:

(a) coating a surface of a porous fibrous web, in which the opposite surface of the web is in contact with a porous substrate sheet, with a liquid dispersion containing es- "Ice sentially a polymeric component and a solvent therefor; the dispersion having a viscosity high enough to permit its retention by the web under the coating conditions and low enough to permit complete penertation of the web under the conditions of step (b) below, the polymeric component having a secant tensile modulus at 5% elongation of above about 600 pounds per square inch (p.s.i.), under the drying conditions of step (d) below,

(b) applying suction to the free surface of the substrate sheet and thereby drawing the dispersion through the porous web and at least partially into the substrate sheet to form a laminate in which the dispersion is distributed within both porous web and substrate sheet and interconnecting them,

(c) bathing the laminate with a liquid which contains a non-solvent for the polymeric components, which nonsolvent is miscible with said solvent, to remove the solvent, and

(d) drying the resulting laminate.

The process can be more readily understood by referring to the figure in which a dispersion 1 of a polymer in a mixture of liquids, one of which is a solvent for the polymer (e.g., dimethyl formamide) and one of which is a non-solvent for the polymer (e.g., water) is extruded through slot 7 of hopper 2 upon a porous interlayer sheet 3 at point B. The interlayer is in contact with a porous substrate 4 and this composite sheet proceeds from left to right in the process. In a very short time interval from B, the composite sheet material, i.e., the coated interlayer 3 in contact with substrate 4, is passed over vacuum roll 8, which extends across the width of the composite sheet material. The reduced pressure in the slot 5 pulls polymer dispersion 1 through porous interlayer 3 and into porous substrate 4 to form a laminate. Preferably, as shown in the figure, two vacuum rolls are used in series, i.e., one after the other with the second vacuum roll 10 having a reduced pressure in slot 9. This second vacuum roll insures that sufficient polymer dispersion 1 is pulled through the porous interlayer 3 and into the substrate 4, and insures that the interlayer 3 is in complete contact with the substrate 4. The position of the second vacuum roll 10 is not critical but the use of this second vacuum roll is preferred since it increases the strength of the bond between the interlayer fabric and the substrate which further reduces the probability of delamination of the microporous laminate when it is used as a shoe upper material.

When a smoothly coated product is desired, as in the case of products to be used for shoe uppers, the quantity of dispersion coating should be such that the composite sheet after passing vacuum roll or rolls still retains sufiicient polymer dispersion on the top surface of interlayer to provide a smooth coating. This coating undergoes a flow-out following passage over vacuum roll or rolls which permits formation of a smooth coating of uniform thickness on the upper surface of the interlayer sheet and without a visually apparent pattern.

Following the flow-out interval which is usually less than about a minute but may be more or less depending upon the viscosity of the dispersion, the laminate is bathed in tank 6 which contains a liquid miscible with the solvent in polymer dispersion 1 but which is a non-solvent for the polymeric material. Optionally the tank can also contain a solvent for the polymer so long as there is sutficient non-solvent to coagulate the polymer during the bathing treatment.

Any porous fibrous sheet can be used as the interlayer 3 or the substrate 4 but sheets having uniform porosity produce the best laminates. These sheet materials can be woven or non-woven and include twills, drills, ducks, jersey, tricot, simplex knitted materials, felts, needle punched batts, porous batts impregnated with synthetic resins, such as rubber and vinyl halide polymers. The particular fibers from which the interlayer or substrate is made is not critical and can be continuous or staple fibers prepared from polyamides, polyesters, polyesteramides, acrylic polymers and other synthetic polymers, also viscose, rayon, wool, cotton, glass and mixtures thereof can be utilized as can be elastomeric fibers and elastic fabrics. Porous non-woven, preferably heat-shrunk batts of poly(ethylene-terephthalate) fibers impregnated with polymers such as disclosed in US. Patent 3,100,721 to Holden, issued Aug. 13, 1963, are particularly preferred porous substrates for use in this invention in the manufacture of microporous materials suitable for shoe uppers as producing exceptionally fine quality products.

In using this invention to prepare non-roughening microporous sheet materials useful for shoe uppers, it is essential that the interlayer fabric utilized have certain physical characteristics including a grab tensile strength of at least one pound/inch, preferably 20200 pounds/ inch and more preferably, 60-80 pounds/inch, a break elongation of 740%, a modulus of ISO-12,000 pounds per square inch at elongation and a thickness of 312 mils. The above values of grab tensile strength, modulus and elongation are obtained according to the test procedure of ASTM-l682-64. Woven fabrics should possess the first two characteristics both in the warp and woof and non-Wovens should exhibit them in any planar direction. In order to prepare the highest quality product, the interlayer fabric should have the following properties: a break elongation of about 30%, a modulus of about 1,000- 5,000 pounds per square inch at 5% elongation and a thickness of about 5 to 8 mils. Several interlayer fabrics can be used in the process of this invention provided the several fabrics together have the aforementioned properties.

Additionally, it is essential in preparing non-roughening products by the process of this invention that the interlayer material have a smoothness factor of not more than 15 mls. By this it is means that 15 mils or less of the dried coating formed from the dispersion utilized in this process that is coated upon the interlayer material will provide a smooth coating which hides (i.e., renders invisible to the naked eye) the pattern and texture of the fabric coated. For purposes of reference herein, the polymer dispersion utilized in Example 1 is taken as a standard polymer dispersion for forming a coating and any fabrics having the above physical properties and which will have its surface pattern hidden with 15 mils or less of a dried coating formed from this dispersion can be used in this invention to prepare microporous sheet materials having superior non-roughening properties.

The polymeric dispersions used in this invention are not critical and can be any dispersion suitable for bonding the interlayer material to the substrate. In utilizing the process of this invention to produce microporous materials suitable for shoe uppers, however, it is a primary requirement that the polymeric component has a secant tensile modulus at 5% elongation of above about 600 pounds per square inch during the entire processing cycle, i.e., from the time the polymeric component is coagulated into a microporous structure until it is dried. Generally, a microporous structure formed from a polymer which in consolidated form has a secant tensile modulus below about 600 p.s.i. collapses as the liquid is being removed or after the liquid is removed from the micropores of the structure so that a relatively impermeable product is formed. Preferably, the secant modulus at 5% elongation of the polymer during the cycle is about 60025,000 p.s.i. and more preferably, about SOD-10,000 p.s.i., and still more preferably, about 800-3000 p.s.i. The secant tensile modulus is the ratio of the stress to the strain at 5% elongation of the sample determined from the tensile stress-strain curve and is expressed as force per unit area, e.g., pound per square inch. The secant tensile modulus measurement is carried out according to ASTM 113-882- 64T modified as described below,

The secant tensile modulus of the polymer useful in this invention is determined by forming a 5 to 20 mil continuous void-free polymer film from the polymeric solution used in the process to form the microporous sheet material of this invention. The film is formed by casting this polymeric solution on a glass plate and the solution is then dried, e.g., at C. for 90 minutes.

The stress-strain curve which is necessary to calculate the secant tensile modulus at 5% elongation of the polymer used in the invention is preferably obtained on an Instron Tensile Tester using a /2 inch wide specimen cut from the above prepared polymeric film With about one inch between grips. The following settings are preferably used on the Instron Tester to obtain a stress-strain curve: chart speed of-l0 inches per minute, cross head speed of 1 inch per minute, and a full scale load of 2 to 5 pounds.

The secant tensile modulus is obtained from the chart of the force vs. strain curve by drawing a line at 5% specimen elongation (strain) parallel to the force axis of the chart. The point at which this line intersects the force/strain curve defines the force in pounds necessary to elongate the specimen 5%. This force value is divided by the initial cross-sectional area of the specimen to give the corresponding stress value in pounds per square inch. This stress value is divided by the strain (0.05) to give the secant tensile modulus to 5% elongation.

To initially select polymers useful in this invention, the test temperature is usually room temperature, about 23 C. At this temperature, polymers potentially useful in this invention have a secant tensile modulus at 5% elongation above about 600 p.s.i. However, as previously stated, polymers useful in this invention have a secant tensile modulus at 5% elongation of above about 600 p.s.i. during the entire process cycle; therefore, the highest temperature used during the process for forming the microporous product should be used as the test temperature, e.g., if the drying temperature is the highest temperature in the process and is C., the secant tensile modulus of a potentially useful polymer should be tested at 110 C. and at this test temperature, the secant tensile modulus at 5% elongation should be above about 600 p.s.i.

The first step in the process of this invention is to form a solution having as essential constituents a polymeric component and a solvent for the polymeric component. This solution may be used directly as the coating dispersion but preferably, a liquid miscible with the solvent but a non-solvent for the polymeric component is admixed with the solution in an amount up to and including the quantity which starts to transform the polymer solution into a substantially colloidal polymeric dispersion. When a substantially colloidal dispersion is used, it should have a viscosity greater than about one poise and a polymer concentration of greater than about 7% by weight. (For purposes of this invention, dispresion is used in its generic sense to include the above-described mixtures of polymer and solvent which are in the form of solutions, mixtures of polymer in solvent and non-solvent in the form of solutions, and colloidal dispersions of polymers in solvent-non-solvent mixtures.) The polymeric dispersion is then coated onto an interlayer sheet as above described and bathed with an inert liquid which contains a non-solvent for the polymeric component and is miscible with the solvent. The resulting product is dried.

Any of a wide variety of polymers can be dispersed in liquids and employed in the instant process. All of the dispersions and polymers and methods for preparing microporous products disclosed in US. Patent 3,100,721 to Holden and US. Patent 3,208,875 to Holden, issued Sept. 28, 1965, are useful in this invention. The entire disclosures of US. Patents 3,100,721 and 3,208,875 are hereby incorporated into and made a part of this specification for the purpose of illustrating materials and procedures useful in this invention.

A preferred major polymeric component useful in this invention for making microporous sheet materials is a polyurethane elastomer made by reacting an organic diisocyanate with an active hydrogen containing polymeric material such as a polyalkyleneether glycol or a hydroxyl-terminated polyester to produce an isocyanate-termi nated polyurethane prepolymer, and reacting the resulting prepolymer with a chain-extending compound having two active hydrogen atoms bonded to amino-nitrogen atoms. A mixture of hydrazine and N-methyl-aminobispropylamine is a preferred chain-extender; however, other chainextenders which are useful include dimethyl-piperazine, 4-methyl-m-phenylenediamine, m phenylene diamine, 1,4-diamino-piperazine, ethylene diamine and mixtures thereof.

The polyurethane polymer useful in this invention can be prepared by first mixing a molar excess of the diisocyanate with the active hydrogen containing polymeric material and heating the mixture at about 50l20 C. until the prepolymer is formed. Or, the diisocyanate can be reacted with a molar excess of the active hydrogen containing polymeric material, and the reaction product capped by reacting it with more diisocyanate to form the prepolymer.

Aromatic, aliphatic and cycloaliphatic diisocyanates or mixtures thereof can be used in forming the prepolymer.

Such diisocyanates are, for example, tolylene-2,4-diisocyanate, tolylene-2,S-diisocyanate, m-phenylene diisocyanate, biphenylene-4,4'-diisocyanate, methylene bis- (4-phenyl isocyanate), 4-chloro-1,3-phenylene diisocyanate, naphthalene-1,5-diisocyanate, tetramethylene- 1,4-diisocyanate, hexamethylene-l,6-diisocyanate, decamethylene-l,10-diisocyanate, cyclohexylene 1,4 diisocyanate, methylene bis(4-cyclohexyl isocyanate) and tetrahydronaphthalene diisocyanate. Arylene diisocyanates, that is, isocyanates in which the isocyanate groups are attached to an aromatic ring are preferred. In general, they react more readily than do alkylene diisocyantes.

A polyalkyleneether glycol is the preferred active hydrogen containing polymeric material for the prepolymer formation. The most useful polyglycols have a molecular weight of 300 to 5,000, preferably 400 to 2,000, and include, for example, polyethyleneether glycol, polypropyleneether glycol, polytetramethyleneether glycol, polyhexamethyleneether glycol, polyoctamethyleneether glycol, polynonamethyleneether glycol, polydecamethyleneether glycol, polydodecamethyleneether glycol and mixtures thereof. Polyglycols containing several different radicals in the molecular chain, such as, for example, the compound HO(CH OC H ),,H wherein n is an integer greater than 1 can also be used.

Polyesters which can be used instead of, or in conjunction with, the polyalkyleneether glycols are, for example, those formed by reacting acids, esters or acid halides with glycols. Suitable glycols are polymethylene glycols, such as ethylene-, propylene-, tetramethylene, decamethylene glycol, substituted polymethylene glycols, such as 2,2-dimethyl-1,3-propanediol, cyclic glycols, such as cyclohexanediol and aromatic glycols, such as xylylene glyclo. Aliphatic glycols are generally preferred when maximum product flexibility is desired. These glycols are reacted with aliphatic, cycloaliphatic or aromatic dicarboxylic acids or lower alkyl esters or ester forming derivatives thereof to produce relatively low molecular weight polymers, preferably having a melting point of less than about 70 C., and molecular weights like those indicated for the polyalkyleneether glycols. Acids for preparing such polyesters are, for example, succinic, adipic, suberic, sebacic, terephthalic and hexahydroterepththalic acids and alkyl and halogen substituated derivatives of these acids.

The chain extension reaction is usually carried out at a temperature below 120 C. and often at about room temperature, particularly for hydrazine-extended polymers. During the reaction, prepolymer molecules are joined together into a substantially linear polyurethane polymer, the molecular weight of which is usually at least 5,000 and sometimes as high as 300,000. The reaction can be carried out without a solvent in heavy duty mixing equipment or it can be carried out in a homogeneous solution. In the latter case, it is convenient to use as a solvent one of the organic solvents to be employed in the polymer solution.

Since the resulting polyurethane polymer has rubberlike elasticity, it is referred to as an elastomer, although the degree of elasticity and rubber-like resilience may vary widely from product to product depending on the chemical structure of the polymer and the materials in combination with it.

A vinyl chloride polymer is another preferred component of the polymer solution when making leatherlike sheet materials. Superior product abrasion resistance is obtainable when a vinyl chloride polymer is used in combination with an elastomer such as the polyurethane described above. When making a shoe upper material or the like from a blend of polyurethane elastomer and vinyl chloride polymer, it is generally preferred to employ a major proportion (over 50 weight percent, preferbly percent) of the polymer and a minor proportion (less than 50 weight percent and preferably 20 percent) of the latter. Useful vinyl chloride polymers include polyvinyl chloride and copolymers of a major proportion, preferably at least 80% of vinyl chloride and a minor proportion of another ethylenically unsaturated monomer, such as vinyl acetate, vinylidene chloride, or diethyl maleate.

Within the secant tensile modulus range specified above, the polymeric component of the solution from which coating is formed can contain one or more of numerous types of polymers, which are exemplified by the following: polyurethanes, vinyl halide polymers, polyamides, polyesteramides, polyesters, polyvinyl butyral, polyalphamethylstyrene, polyvinylidene chloride, alkyl esters of acrylic and methacrylic acids, chlorosulfonated polyethylene, copolymers of butadiene and acrylonitrile, cellulose esters and ethers, polystyrene and other polymers made from monomers containing vinyl groups. Synthetic organic polymers are generally preferred and elastomeric polymers or relatively high molecular weight are especially preferred.

When a polymer is used which is known to be compatible with plasticizers, for example, a vinyl chloride polymer, it can be blended with known plasticizers therefor in an amount up to but not including the amount which causes the secant tensile modulus at 5% elongation to drop below 600 psi. Other known additives for polymeric compositions can also be added to the polymeric component, such as pigments, fillers, stabilizers and antioxidants.

The polymer component selected is dissolved in enough solvent to yield a solution having the desired solids content and viscosity. For doctor-knife application, it is usually preferred to use a solution which, after addition of non-solvent if any is employed in the solution, has a polymer content of about 1030 weight percent and a viscosity of about l0500 poises. The organic solvent used in the solution as well as in the coagulation bathing step should be one that is miscible, preferably, completely miscible, with the non-solvent liquid to be used in practicing the invention. N,N-dimethyl formamide is a preferred solvent for the polymers soluble therein in view of its high solvent power for many of the preferred polymers as well as its high miscibility with the generally preferred non-solvent liquids including water. Other useful solvents include dimethyl sulfoxide, tetrahydrofuran, tetramethyl urea, N,N-dimethyl acetamide, N-methyl-2 pyrrolidone, ethyl acetate, dioxane, butyl carbinol, phenol, chloroform and gamma-butyrolactone. Also useful are blends of these solvents with various water-miscible liquids, such as ketones and alcohols which alone are often poor solvents for the polymer. One very useful blend is composed of dimethyl formamide and methyl ethyl ketone.

When the solvent is to be removed from the applied layer merely by drying, it should be more volatile than the non-solvent used in the process.

Having prepared the polymer dispersion, an optional but generally preferred step is to admix with the solution a non-solvent for the polymer, the non-solvent being a liquid that is at least partially miscible with the organic solvent in the solution. Non-solvents which can be admixed with the polymer solution in accordance with the present method include water, ethylene glycol, glycerol, glycol monoethyl ether, hydroxyethyl acetate, tertiary butyl alcohol, 1,1,l-trimethylol propane, methanol, ethanol, hexane, benzene, naphtha, toluene, tetrachloroethylene, chloroform and the like. When operable, water and blends thereof With water-miscible liquids are usually preferred.

Before the water or other non-solvent is added to the polymer solution, it is preferably blended with a substantial proportion, for example, from about 2 to 5 times its own weight, of an organic solvent of the type used in preparing the polymer solution. Addition of the nonsolvent to the solution should be done gradually and with stirring to prevent localized coagulation.

The non-solvent is added in an amount up to and including the amount which starts to transform the solution into a substantially colloidal dispersion of polymer particles. The preferred amount of non-solvent to add is usually about 40l00% on this basis, and still more preferably about 70l00% of the amount required to bring about initial indications of a hazy colloidal dispersion. If the polymer solution was clear initially, it will normally still be substantially clear after the non-solvent has been added in the practice of this invention.

It is sometimes desirable to add a thickening agent to the polymer solution before it is applied to the substrate so as to cause an increase, preferably a considerable increase, in the solution viscosity. This is especially desirable when using a solution to which little or no nonsolvent is added.

One reason it is usually preferable in the present invention to add non-solvent to the polymer solution at least to the 40l00% range mentioned above, is that it helps insure against the formation of macrovoids in the coating, particularly when the substrate is a fibrous sheet having relatively low liquid permeability and the coated material is quickly immersed in the bathing liquid.

Another reason it is usually preferable to add nonsolvent to the polymer solution in the 40l00% range, based on the amount needed to cause initial transformation of the coating composition from a solution to a colloidal dispersion, is that faster coagulating conditions can be used in the coagulation bathing step without interference with the attainment of a product that is finely microporous, highly vapor permeable and resistant to damage by repeated flexing. However, under some circumstances it will be preferable to add little or no nonsolvent to the coating solution; for example, when it is permissible or desirable to use slow coagulation techniques or when the emphasis is on properties other than those just listed.

An experienced operator will have little difficulty in estimating the best amount of non-solvent to be added to a solution of a particular type of polymer for the production of a particular type of product. An inexperienced operator can readily predetermine a desirable non-solvent range by making a small trial run. For example, he can add to five small samples of the main body of solution 30%, 60%, 80% and 90%, respectively, of nonsolvent, based on the previously determined amount needed to cause initial transformation of the coating composition from a solution to a colloidal dispersion, complete the process in accordance with the teaching herein and according to his best judgment, select the sample product best fitted to the intended use, and calculate the proportionate amount of non-solvent he wishes to add to the main body of the solution.

After the non-solvent, if any, has been added to the polymer solution, a layer of the resulting dispersion is applied to the interlayer web. Coating methods which are useful for applying the layer are exemplified by doctorknifing, extruding, dipping, spraying, brushing and rollercoating.

When the coating dispersion is in the form of a substantially colloidal dispersion, coagulation of the polymeric component is effected by bathing With a liquid which is a non-solvent for the polymer but miscible With the solvent utilized present in the dispersion. If the dispersion solvent is miscible with water, then the latter is a convenient bathing liquid.

When the coating dispersion is a solution and, there fore, contains less non-solvent than is necessary to bring it to the point of transformation to a substantially colloidal dispersion, coagulation is effected by bathing with a mixture of a solvent for the polymer and a non-solvent for the polymer, the non-solvent being at least partially miscible with the solvent. In this case, the solventznonsolvent weight ratio in the bathing mixture should be about from 10:90 to 95:5. Useful solvents and non-solvents have been listed above in connection with preparing the polymer solution. It is usually preferred to use a bathing mixture having a solvent content of at least weight percent. An organic solventznon-solvent ratio in the coagulation bathing step substantially above 95:5 is to be avoided in any event to prevent the bathing mixture from having a solvent action on the coating to the extent of either preventing a sufficient coagulating effect to yield micropores or causing any pores formed to collapse.

At the other extreme, when the polymer dispersion is a solution, particularly with the preferred polyurethanes and polyvinyl chloride resins and blends thereof, there is usually no advantage in using less solvent in the coagulation bath than that needed to give a solventznon-solvent ratio of :30; this is true even when as much as about of non-solvent has been added to the polymer solution based on the amount that would cause initial transformation of the solution to a colloidal dispersion. This is not to say, of course, that with certain polymer solutions or with specific process conditions it will not be desirable or useful to have a solvent:non-solvent ratio of less than 70:30, or of less than 50:50. However, as a general rule, there is more of a tendency towards pore collapse at the lower ratios. As indicated previously, the desired pore formation can often be controlled by other measures, one of the most practical measures being to raise the temperature of the first bath substantially above room temperature, say to about 40-60 C. With a colloidal dispersion of polymer, a first bath temperature of about normal room temperature to 25 C. is suitable for this purpose.

Preferably the web coated with the polymer dispersion is bathed by immersion in the bathing liquid or by first floating it inverted thereon. However, this bathing step can also be performed by subjecting the layer to a spray or a vapor of the bathing liquid, or by a combination of these and other known bathing techniques. Bathing is intended to mean causing the bathing liquid, either in the form of a unitary body or in finely divided form, such as a spray or vapor, to come in contact with the polymer dispersion layer.

The reduced pressure applied to the underside of substrate 4 at slot 5 in the figure can range from about 0 to 29 inches of mercury (absolute) depending upon the thickness and porosity of the substrate and interlayer sheets, the viscosity of the polymeric dispersion and the degree of penetration desired. Usually and preferably 10-27 inches of mercury, absolute, are utilized. In the manufacture of microporous material a sufficiently low pressure is normally applied so that during the time interval in which a given area of substrate is exposed to this reduced pressure, the coating dispersion will be drawn substantially into, but not entirely through, the substrate, leaving a smooth coating upon the upper surface of interlayer 3, the coating being 220 mils thick after coagulation.

It is important in the process of this invention that the time interval between extrusion of the polymeric dispersion onto the interlayer sheet and the bathing step be controlled so that any absorption of moisture from the atmosphere does not result in undesirable coagulation of the polymeric component prior to bathing. In any event, the non-solvent content of the polymeric dispersion in the extrusion hopper can be adjusted to compensate for the amount of moisture change which occurs in the coating during this time interval. The uniformity of the microporous product will thereby be promoted.

The following examples illustrate the invention. Parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1 Utilizing the apparatus of the figure, a substrate 4 consisting of a porous impregnated needle punched nonwoven mat of 125 denier heat shrunk polyethylene terephthalate staple fibers is brought into contact with interlayer sheet 3 consisting of a woven 5.00 x 40 cotton lawn fabric having the following characteristics: count 123/118; weight 2.6 oz./yd. grab tensile strength 50 x 50 lbs./in.; break elongation 15 x 15%; modulus 720 x 1200 lbs/in. at elongation; thickness 5 mils and smoothness factor 13 mils. The non-woven fibrous substrate had been previously impregnated with a polyurea dispersion composition similar to that utilized below and then dried, so that the impregnated substrate contained 50% dispersion solids based on the weight of fibers.

From hopper 2, a 12 /2% solids polyvinyl chloride/polyurea dispersion in dimethylformamide and water, and prepared in accordance with Example 1 of U.S.P. 3,100,721 to Holden, is extruded on interlayer sheet 3 at B in the amount of 3.75 pounds dispersion per square yard of surface coated and the coated structure is then passed over a vacuum roll 8 and subjected to the reduced pressure (about 5 inches of mercury vacuum) through slot 5 (about /2 inch in width) as the composite structure of substrate, interlayer and dispersion passes over slot 5. During the time that the layered structure is exposed (about 0.25 second) to reduced pressure provided by vacuum slot 5, polymeric dispersion is pulled through interlayer sheet 3 and into substrate 4. In about seconds, the layered structure passes over a second vacuum roll 10 and again is subjected to reduced pressure (about 5 inches of mercury vacuum) for about 0.25 second through vacuum slot 9 positioned in the vacuum roll 10. This second vacuum pulls the coated interlayer into firm contact with the substrate and prevents any possible delamination.

However, sufiicient polymer dispersion coating remains on the upper side of interlayer sheet 3 to provide a coat ing mils thick after coagulation. About 38 seconds after leaving the initial reduced pressure zone (slot 5), the laminated structure is immersed in tank 6 which contains water at room temperature and is bathed in this water for about three minutes. Finally, the resulting product is immersed in another water bath at C. until the polymer is completely coagulated. Residual solvent is leached from the product by further bathing and then the coated substrate is subjected to hot air at 120 C. for 7 minutes followed by drying at about C. temperature. The resulting product is a microporous structure having a smooth adherent uniformly microporous coating about 0.013 inch thick and with a water vapor permeability value (often referred to as LPV or leather permeability value) of about 8000 grams of water per hour per 100 square meters determined by the test described by Kanagy 10 and Vickers in the Journal of Leather Chemists AssociatiOn, 45, 211-242 (Apr. 9, 1950).

The tensile strength of the adhesive bond between the interlayer and substrate in the microporous product is determined by taking a 1" x 6" sample and cutting it across the width sufliciently deep so that the interlayer could be separated from the substrate for a length of about 2 inches. The sample is then placed in an Instron tensile strength tester and the tensile strength of the adhesive bond is measured using a cross-head speed of 10 inches per minute, a chart speed of 2 inches per minute and a jaw gap of 2 inches. Tensile strength of the bond is 4.5 pounds per inch.

The roughening characteristics of the microporous material produced in this example is 0 and is determined by clamping a twelve inch square sample tightly between ring clamps, coating side up and distending the material upwards by a plano-convex deformation head to a maximum of one inch above the original plane. The head is moved by hydraulic pressure over a period of about 15 seconds. If there is no apparent roughness at the high point, the roughness value is 0; if discernible but insignificant roughness is present, the roughness value is 1; if more than insignificant roughness is apparent to the naked eye, the roughness value is greater than one.

EXAMPLE 2 The procedure of Example 1 is repeated except that the cotton fabric interlayer is replaced with a woven fabric containing poly(ethylene terephthalate) fibers and 35% cotton, the fabric having a count of 96 x 96 (Greige). The fabric is bleached, desized, double singed each side and then stretched while wet from an initial width of 47 inches to a final width of 49 inches using a tenter frame. By this procedure, the fabric which initially had a grab tensile strength of 55 x 60 lbs./in., a modulus of 17 x 6 pounds at 5% elongation and a break elongation of 26% x 32% is converted to a fabric having a grab tensile strength of 55 x 54 pounds per inch, a modulus of 10 x 7 pounds at 5% elongation, a break elongation of 25% x 25%, a smoothness factor of 14 mils, thickness 5.5 mils and weight 2.3 oz./yd. The microporous material produced using this interlayer has a surface coating 14 mils thick and when tested according to Example 1, exhibits no roughness even when fully distended, an adhesive strength of 4.5 pounds per inch between layers, and a leather permeability value of about 7000 grams of water per hour per 100 square meters.

EXAMPLE 3 The procedure of Example 1 is followed except that the woven cotton interlayer is replaced by a non-woven fabric composed by poly(ethylene terephthalate) continuous filaments separately and randomly disposed within the fabric and prepared using an apparatus similar to that described in Example 2 of Belgian Patent 608,646. The non-woven fabric is prepared by melt spinning poly- (ethylene terephthalate) having a relative viscosity of about 34 into filaments from a 68 hole spinneret (7 mil hole diameter) while an /20 ethylene terephthalate/ isophthalate copolymer is cospun from an adjacent 34 hole spinneret. Thirteen grams of copolymer are spun for each 78 grams of poly(ethylene terephthalate). The freshly spun filaments are passed in rubbing contact with chromic oxide guide bars to give them an induced electrical charge. An aspirating air jet operating at 50 p.s.i.g. pressure is employed to attenuate and quench the filaments, advance them to an aluminum plate receiver and lay them down on the receiver in separate and random fashion in the form of a loosely constructed nonwoven batt. The receiver is moved sufiiciently to yield a batt of uniform thickness.

Next the batt is placed between two sheets of paper and pressed together under a pressure of seven p.s.i.g.

1 1 at 160 C. to consolidate it. The consolidated fabric is denser and stronger than before but is still substantially entirely unbonded. The non-woven fabric has the following characteristics: minimum grab tensile strength 20 lbs./in.; break elongation 55% x 35%; modulus at 15% elongation 300 x 500 lbs./in. thickness 5 mils; weight 1.6 oz./yd. The non-woven fabric has a smoothness factor of 3 mils, by which it is meant that as little as 3 mils of a dried coating formed from the collodial dispersion utilized in Example 1, provides a smooth coating which to the naked eye is free from the surface pattern exhibited by the non-woven fabric prior to coating.

The consolidated fabric is then utilized in the procedure of Example 1 to provide a surface coating 8 mils thick after coagulation. The resulting microporous product is 35 mils thick having no roughness even when fully distended under the test described in Example 1. Its adhesive strength between layers is 6 pounds per inch, and it has an LPV similar to that of Example 2.

The roughness tester utilized in the above examples is Model 1004-50B made by Columbia Vise and Manufacturing Company, Cleveland, Ohio. Thickness of fabrics is determined in accordance with ASTM D-1813-60-T.

I claim:

1. A process for producing a nonroughening microporous laminate which comprises:

(a) coating a surface of a porous flexible fibrous web with a liquid dispersion containing essentally a polymeric component and a solvent therefore, the dispersion having a viscosity high enough to permit its retention by the web under the coating conditions and low enough to permit complete penetration of the web under the conditions of step (b) below, the polymeric component having a secant tensilemodulus at 5% elongation above about 600 pounds per square inch, under the drying conditions of step (d) below, said web having a grab tensile strength of at least one pound/inch, a break elongation of 740%, a modulus of 150-12,000 lbs/in. at 5% elongation, a thickness of 3-12 mils and a smoothness factor not exceeding mils, and the other surface of said web being in contact with a flexible, porous, fibrous substrate;

(b) applying suction to the free surface of the substrate sheet and thereby drawing the dispersion through the porous web and at least partially into the substrate sheet to form a laminate;

(c) bathing the laminate with a liquid which contains a non-solvent for the polymeric component, which non-solvent is miscible with said solvent, to coagulate the polymeric component into a microporous structure and remove solvent; and

(d) drying the resulting laminate.

2. The process of claim 1 in which suction is applied to the free surface of the substrate at two separate points before said laminate is bathed in a non-solvent for the polymeric component to coagulate the polymeric component and remove solvent.

3. The process of claim 1 in which the porous fibrous web is a woven cotton fabric.

4. The process of claim 1 in which the porous fibrous web is a woven fabric containing cotton and polyester fibers in a weight ratio of about :65.

5. The process of claim 1 in which the porous fibrous web is a non-woven fabric consisting essentially of polyester fibers.

6. The process of claim 1 in which the polymeric component comprises a polyurethane.

7. The process of claim 4 in which the polymeric component comprises a vinyl chloride polymer-polyurethane mixture containing at least 50% polyurethane by weight.

8. The process of claim 1 in which the liquid dispersion is a dispersion of a polymer in dimethyl formamide and water.

9. The process of claim 8 in which the dispersion is a colloidal dispersion and the polymeric component is a polyurethane having a secant tensile modulus at 5% elongation of about 800-3000 pounds per square inch.

10. The process of claim 8 in which the dispersion is a colloidal dispersion of a vinyl chloride polymerpolyurethane mixture containing at least 50% polyurethane by weight and having a secant tensile modulus at 5% elongation of about 800-3000 pounds per square inch.

11. A microporous laminate consisting essentially of (1) a porous substrate fabric, (2) a porous fibrous interlayer web superposed on the substrate, and (3) a uniformly microporous polymeric composition forming a continuous matrix within the interstices of the interlayer web and the interstices of the substrate and terminating in a smooth microporous coating on the interlayer webs exterior surface, the interlayer web being a fabric having a grab tensile strength of at least one pound/inch, a break elongation of 740%, a modulus of 15012,000 lbs/in. at 5% elongation, a thickness of 312 mils and a smoothness factor not exceeding 15 mils.

12. The laminate of claim 11 characterized by a delamination tensile strength of at least 3.0 lbs/in. and a roughness factor not exceeding one.

13. The laminate of claim 12 in which the interlayer fabric is a woven cotton fabric.

14. The laminate of claim 12 in which the interlayer is a woven fabric of mixed polyester and cotton fibers.

15. The laminate of claim 14 in which the polyester fibers are composed predominantly of poly(ethylene weight ratio of polyester to cotton fibers in the interlayer is about /35.

16. The laminate of claim 12 in which the interlayer is a non-woven web of randomly disposed synthetic fibers.

17. The laminate of claim 16 in which the synthetic fibers are polyester fibers.

18. The laminate of claim 17 in which the polyester fibers are composed predominantly of poly(ethylene terephthalate), the remainder being composed of poly- (ethylene terephthalate/isophthalate).

References Cited UNITED STATES PATENTS 2,940,871 6/1960 Smith-Johannsen l1763 3,042,573 7/1962 Roberts 156285 3,100,721 8/1963 Holden 1l7135.5

ROBERT F. BURNETT, Primary Examiner.

R. L. MAY, Assistant Examiner.

US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,418,198 December 24, 1968 Robert V. Einstman It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 12, line 40, "fibers are composed predominantly of poly(ethylene" should read fibers are po1y(ethy1ene terephthalate) fibers and the Signed and sealed this 17th day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

